If a line already contains plain characters (even whitespace, say everything
whitout a special function like tags etc) then an equal sign will only be
an equals sign not the start of ruby code.
The main features of Haml can be correctly parsed according to
http://haml-lang.com/docs/yardoc/file.HAML_REFERENCE.html.
There exist some limitations inherently comming from the limitations
of state machine based highlighters (without side effects)... this parsers
sucks with multiline comments, strings etc since the indent based grouping
can't be evaluated.